JP7629409B2 - Systems and methods for producing carbon nanotubes - Patents.com - Google Patents

Description

RELATIONSHIP TO RELATED APPLICATIONS This application claims priority to U.S. Provisional Patent Application No. 62/828,981, filed April 3, 2019, the entire contents of which are incorporated herein by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT: None

FIELD This disclosure relates generally to systems and methods for producing carbon nanotubes from flare gases and other gaseous carbon-containing sources.

2. Background Current methods for forming carbon nanotubes rely on expensive commercial grade natural gas (mainly methane and some ethane, butane and propane) as a carbonaceous source that reacts to form carbon nanotubes and hydrogen. It would be advantageous to have a system and process that takes cheap carbonaceous sources such as oil-gas extraction, refineries, chemical plants, coal mining and landfills and converts them into more expensive products such as carbon nanotubes and hydrogen gas.

1 illustrates a schematic diagram of a CVD system for the production of carbon nanotubes. FIG. 1B illustrates a schematic diagram of an injector apparatus for use in conjunction with the CVD system illustrated in FIG. 1A.

Before describing at least one embodiment of the present disclosure in detail, it is to be understood that the disclosure is not limited in its application to the details of the construction and arrangement of the components or steps or methodology set forth in the following description. The disclosure is capable of other embodiments, i.e., of being practiced or carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting.

Unless otherwise specified herein, technical terms used in connection with this disclosure shall have the meanings commonly understood by those of ordinary skill in the art. Further, unless the context otherwise requires, the singular includes the plural and the plural includes the singular.

All patents, published patent applications, and non-patent publications mentioned in this specification are indicative of the level of skill of those skilled in the art to which this disclosure pertains. All patents, published patent applications, and non-patent publications cited in any part of this application are expressly incorporated by reference in their entirety to the same extent as if each individual patent or publication was individually and specifically incorporated by reference and to the same extent that they do not contradict this disclosure.

All of the compositions and/or methods disclosed herein can be made and executed without undue experimentation in light of the present disclosure. While the compositions and methods of the present disclosure have been described in terms of embodiments or preferred embodiments, it will be apparent to one of ordinary skill in the art that changes can be applied to the compositions and/or methods described herein, and to the steps or sequence of steps of the methods, without departing from the concept, spirit, and scope of the present disclosure. All such similar substitutions and modifications apparent to those of ordinary skill in the art are deemed to be within the spirit, scope, and concept of the present disclosure.

Any aspect herein relating to carbon nanotubes may also be modified within the spirit and scope of the present disclosure to substitute other tubular nanostructures, including, for example, inorganic or mineral nanotubes. Inorganic or mineral nanotubes include, for example, silicon nanotubes, boron nanotubes, and carbon nanotubes with heteroatom substitutions within the nanotube structure.

As used in accordance with this disclosure, the following terms, unless otherwise specified, shall be understood to have the following meanings:

The use of the terms "a" or "an", when used in connection with the terms "comprising", "including", "having" or "containing" (or variations of such terms), means "one", but is also consistent with the meanings of "one or more", "at least one" and "one or more than one".

The use of the term "or" is used to mean "and/or" only when alternatives are clearly indicated and only when the alternatives are mutually exclusive.

Throughout this disclosure, the term "about" indicates that a value includes the inherent variation of error of the device, mechanism, or method of determining, or the inherent variation that exists between the subject(s) being measured. For example, and not by way of limitation, when the term "about" is used, the indicated value to which it refers may vary by plus or minus 10 percent, or 9 percent, or 8 percent, or 7 percent, or 6 percent, or 5 percent, or 4 percent, or 3 percent, or 2 percent, or 1 percent, or one or more fractions therebetween.

The use of "at least one" is understood to include 1 as well as any amount greater than 1, including but not limited to 1, 2, 3, 4, 5, 10, 15, 20, 30, 40, 50, 100, etc. The term "at least one" can extend up to 100 or 1000 or more depending on the term to which it refers. Furthermore, the amount of 100/1000 is not to be considered limiting, as lower or higher limits may also produce satisfactory results.

Additionally, the phrase "at least one of X, Y, and Z" is understood to include X alone, Y alone, and Z alone, as well as any combination of X, Y, and Z. Similarly, "at least one of X and Y" is understood to include X alone, Y alone, and any combination of X and Y. Additionally, the phrase "at least one" can be used with any number of components and can have the same meaning as above.

The use of ordinal terminology (i.e., first, second, third, fourth, etc.) is solely for the purpose of distinguishing between two or more items and does not imply any ordering, sequence or importance of one item relative to another or additional ordering unless otherwise stated.

As used herein, the terms "comprising" (and any of its forms, e.g., "comprise" and "comprises"), "having" (and any of its forms, e.g., "have" and "has"), "including" (and any of its forms, e.g., "includes" and "include"), or "containing" (and any of its forms, e.g., "contains" and "contain") are inclusive, i.e., open-ended, and do not exclude additional, unreferenced elements or method steps.

As used herein, the phrases "or combinations thereof" and "and combinations thereof" refer to all permutations and combinations of the listed items preceding the term. For example, "A, B, C or combinations thereof" is intended to include at least one of: A, B, C, AB, AC, BC, or ABC, and, if order is important in the particular context, at least one of BA, CA, CB, CBA, BCA, ACB, BAC, or CAB. Expressly included following this example are combinations that include repetition of one or more items or terms, such as BB, AAA, CC, AABB, AACC, ABCCCC, CBBAAA, CABBB, etc. One of skill in the art will understand that there is generally no limit to the number of items and terms in any combination unless the context clearly indicates otherwise. In the same spirit, the terms "or combinations thereof" and "and combinations thereof," when used in conjunction with the phrase "selected from" or "selected from the group consisting of," refer to all permutations and combinations of the listed items preceding the phrase.

Phrases such as "in one embodiment," "in an embodiment," "according to one embodiment," and the like generally mean that the particular feature, structure, or characteristic that follows the phrase is included in at least one embodiment of the disclosure, and may be included in more than one embodiment of the disclosure. Importantly, such phrases are open-ended and do not necessarily refer to the same embodiment, but of course can refer to one or more preceding and/or following embodiments. For example, in the appended claims, any of the claimed embodiments may be used in any combination.

As used herein, the terms "wt. %, "wt. %, "weight percent" or "percent by weight" are used interchangeably.

As used herein, the term "flare gas" refers to a mixture of gases that is typically burned or flared during oil-gas production or from operations in refineries, chemical plants, coal mining, and landfills. The composition of flare gas depends on its source, but may comprise one or more of the following carbonaceous gases: methane, ethane, propane, n-butane, isobutane, n-pentane, isopentane, neo-pentane, n-hexane, ethylene, propylene, and 1-butene, as well as one or more other components such as carbon monoxide, carbon dioxide, hydrogen sulfide, hydrogen disulfide, hydrogen, oxygen, nitrogen, and water. Flare gas from oil-gas production sites contains primarily natural gas, with more than 90% methane.

As used herein, "carbon nanotubes" is used to refer to single-walled, double-walled and/or multi-walled carbon nanotubes having diameters of less than about 1 nm to about 20 nm and lengths of 1 mm to 5 mm.

As used herein, "carbon nanotube fiber" refers to a staple fiber comprising a number of carbon nanotubes interconnected to form a structure having a diameter in the range of 0.1 to 10 microns and a length of about 150 mm to about 500 mm.

As used herein, "short carbon nanotube fibers" refers to carbon nanotube fibers having a length of only about 1 mm to about 50 mm.

In one aspect, the disclosure is directed to a method for producing carbon nanotubes comprising: (i) introducing a carbonaceous gas, a catalyst, and hydrogen into a reaction vessel, where the reaction vessel (in the presence of the catalyst) is at a temperature sufficient to decompose the carbonaceous gas into constituent atoms of the carbonaceous gas, including carbon and hydrogen, and (ii) interacting carbon atoms of the carbonaceous gas with the catalyst to produce carbon nanotubes.

In another aspect, the disclosure is directed to a method for producing carbon nanotubes comprising the steps of: obtaining a flare gas comprising a carbonaceous source; processing the flare gas; introducing the flare gas, a catalyst, and hydrogen into a reaction vessel, where the reaction vessel (in the presence of the catalyst) is at a temperature sufficient to decompose the carbonaceous gas into constituent atoms of the carbonaceous gas, including carbon and hydrogen; interacting carbon atoms of the carbonaceous gas with the catalyst to produce carbon nanotubes; and recovering the carbon nanotubes.

The flare gas can be obtained from an oil or gas production site, a refinery, a chemical plant, a coal plant, or a landfill. In one embodiment, the system used to produce carbon nanotubes is an on-site oil or gas production site, a refinery, a chemical plant, a coal plant, or a landfill, so that the flare gas can be obtained directly from the source and treated prior to being introduced into the reactor.

The step of treating the flare gas comprises subjecting the flare gas to one or more processes for removing excess hydrogen sulfide, hydrogen disulfide, carbon dioxide and/or carbon monoxide therefrom. As used herein, "excess" means an amount sufficient to cause the flare gas to be considered sour gas and to have a detrimental effect on the ability to produce carbon nanotubes.

In one embodiment, excess hydrogen sulfide means greater than 50% by weight of the total weight of the flare gas, or greater than 40% by weight, or greater than 30% by weight, or greater than 20% by weight, or greater than 10% by weight, or greater than 5% by weight, or greater than 1% by weight, or greater than 0.1% by weight.

In one embodiment, excess carbon dioxide means greater than 50% by weight of the total weight of the flare gas, or greater than 40% by weight, or greater than 30% by weight, or greater than 20% by weight, or greater than 10% by weight, or greater than 5% by weight, or greater than 1% by weight, or greater than 0.1% by weight.

In one embodiment, excess carbon monoxide means greater than 50% by weight of the total weight of the flare gas, or greater than 40% by weight, or greater than 30% by weight, or greater than 20% by weight, or greater than 10% by weight, or greater than 5% by weight, or greater than 1% by weight, or greater than 0.1% by weight.

In one embodiment, excess hydrogen disulfide means greater than 50% by weight of the total weight of the flare gas, or greater than 40% by weight, or greater than 30% by weight, or greater than 20% by weight, or greater than 10% by weight, or greater than 5% by weight, or greater than 1% by weight, or greater than 0.1% by weight.

In one particular embodiment, the treated flare gas contains (i) hydrogen sulfide in an amount of less than 50% by weight, or less than 40% by weight, or less than 30% by weight, or less than 20% by weight, or less than 10% by weight, or less than 5% by weight, or less than 1% by weight, or less than 0.1% by weight of the total weight of the flare gas; and (ii) carbon dioxide in an amount of less than 50% by weight, or less than 40% by weight, or less than 30% by weight, or less than 20% by weight, or less than 10% by weight, or less than 5% by weight, or less than 1% by weight, or less than 0.1% by weight of the total weight of the flare gas. (iii) carbon monoxide in an amount of less than 50% by weight, or less than 40% by weight, or less than 30% by weight, or less than 20% by weight, or less than 10% by weight, or less than 5% by weight, or less than 1% by weight, or less than 0.1% by weight of the total weight of the flare gas; and/or (iv) hydrogen disulfide in an amount of less than 50% by weight, or less than 40% by weight, or less than 30% by weight, or less than 20% by weight, or less than 10% by weight, or less than 5% by weight, or less than 1% by weight, or less than 0.1% by weight of the total weight of the flare gas.

The step of treating the flare gas may include at least one of: (i) electrochemically reducing at least a portion of the hydrogen sulfide to sulfur and then removing it; and (ii) oxidizing at least a portion of the hydrogen disulfide to sulfuric acid and then removing it.

The step of treating the flare gas may alternatively or additionally include a process or system in which at least a portion of the carbon monoxide and/or carbon dioxide is scrubbed from the flare gas. In one embodiment, a portion of the carbon monoxide and/or carbon dioxide may be scrubbed from the flare gas by contacting the flare gas with a solvent, including, for example and without limitation, an amine solvent, such that a portion of the carbon monoxide and/or carbon dioxide is absorbed into the solvent. However, one skilled in the art will recognize that other processes for removing carbon dioxide and/or carbon monoxide from the flare gas may exist and are within the scope of the present disclosure.

The temperature of the reactor can range from 800°C to greater than 1400°C, or from 800(C to 1500°C, or from 900°C to 1400°C, or from 1000°C to 1400°C, or from 1100°C to 1300°C, or about 1200°C at ambient pressure.

In one embodiment, a portion of the carbonaceous gas in the reactor does not interact with the catalyst to form carbon nanotubes. This portion of the carbonaceous gas is then separated and removed from the reactor and sent to a second reactor, optionally along with an additional amount of natural gas or treated or untreated flare gas.

The catalyst mass can also be recovered from the reactor and, optionally, regenerated and introduced into the second reactor with or without a fresh (i.e. unused) catalyst mass.

In one embodiment, the catalyst is regenerated by at least one of: (i) oxidizing the catalyst in air and/or exfoliating the catalyst by electrochemical treatment, dissolving the catalyst in hydrochloric acid to form a hydrochloride salt, and then reacting the hydrochloride salt with sodium cyclopentadienide; and (ii) heating the catalyst to at least 2000°C to volatilize the catalyst, and then depositing the volatilized catalyst.

This process of taking unreacted carbonaceous gas from each reactor and combining it with fresh, regenerated and/or aged catalyst in additional reactors can be carried out one or more times.

In one particular embodiment, the hydrogen formed from the decomposition of the carbonaceous gas is separated and either recovered for storage or resale, used as fuel to heat the reactor, and/or introduced to another reactor.

In another aspect, the carbon nanotubes formed in the reaction vessel are subjected to impact with (i) one or more high velocity jets of gas, (ii) one or more spinning impellers, (iii) a gas stream over a textured surface, and/or (iv) an array of blunt objects prior to exiting the reaction vessel, such that the carbon nanotubes are in the form of short carbon nanotube fibers having lengths ranging from 1 mm to about 50 mm, or more preferably about 25 mm.

Typically, methods for producing carbon nanotube fibers attempt to promote aggregation of the carbon nanotubes in as close to laminar a flow as possible to form very long fibers. It has been found that subjecting the carbon nanotubes to a gas flow and other disruptions of the carbon nanotubes' aggregation ability (e.g., contact with a rotating impeller or impact with a blunt object) allows for the formation of a dispersion suitable for short carbon nanotube fibers, and short carbon nanotube fibers useful for producing other products.

The method for producing carbon nanotubes may further include aspects of the methods and systems described in U.S. Pat. Nos. 7,993,620 and 9,061,913, which are incorporated herein by reference in their entireties.

In particular, the method may include using a system 10 as illustrated in FIG. 1A, which in one embodiment includes a housing 11 (i.e., furnace) having opposing ends 111 and 112, and a passageway 113 extending between the ends 111 and 112. A tube 12 (i.e., reactor) in which extended length nanostructures can be produced may be located within the passageway 113 of the housing 11. As illustrated in FIG. 1A, the ends 121 and 122 of the tube 12 may be positioned to extend from the ends 111 and 112 of the housing 11, respectively. In an embodiment, the housing 11 may include a heating element or mechanism (not shown) for generating the temperature required to grow carbon nanostructures within the tube 12, from about 1100° C. to about 1500° C. Because the heating element must maintain the temperature environment within the tube 12 within a specific range during the synthesis of the extended length nanostructures, not specifically illustrated, the system 10 may include a thermocouple outside the tube 12 for monitoring the temperature environment within the tube 12. In an embodiment, management of the temperature range within the tube 12, for example from about 1000° C. to about 1400° C., can be optimized through the use of an insulating structure 123. In one embodiment, the insulating structure 123 can be made, for example, from zirconia ceramic fibers (e.g., zirconia-stabilized boron nitride). Of course, other insulating materials can also be used.

Because the housing 11 and tube 12 must withstand variations in temperature and gas-reactive environments, the housing 11 and tube 12 must be manufactured from a strong, substantially gas-impermeable, substantially corrosion-resistant material. In an embodiment, the housing 11 and tube 12 can be made from a quartz material. Of course, other materials can be used so long as the housing 11 and tube 12 remain impermeable to gases and maintain their non-corrosive properties. Also, although specifically described as being cylindrical in shape, the housing 11 and tube 12 can be provided in any geometric cross-section.

The system 10 can also include a collection unit 13 in fluid communication with the end 122 of the tube 12 for collecting nanostructures generated from within the tube 12. At the opposite end 121 of the tube 12, the system 10 includes an injector device 14 (i.e., a sprayer) in fluid communication with the tube 12. In an embodiment, the injector 14 can be designed to receive a fluid mixture of components necessary for the growth of nanostructures within the tube 12 from a reservoir 15. The injector 14 can also be designed to volatilize or fluidize the mixture (i.e., generate small droplets) before directing the mixture into the tube 12 for the generation and growth of nanostructures.

In one embodiment, the fluid mixture can include, among other things, (a) a catalyst precursor (i.e., catalyst) on which catalyst particles can subsequently be generated for growth of nanostructures, (b) a conditioner compound for controlling the size distribution of the catalyst particles generated from the catalyst precursor, and thus the diameter of the nanostructures, and (c) a carbonaceous source (including, for example, (i) treated or untreated flare gas, (ii) methane, ethane, butane, and/or propane, (iii) natural gas, and/or (iv) other hydrocarbons such as xylene, toluene, and benzene) for carbon atoms to be deposited on the catalyst particles to grow the nanostructures.

Examples of catalyst precursors from which catalyst particles can be produced can include materials such as ferrocene, iron, iron alloys, nickel or cobalt, their oxides, or their alloys (or compounds with other metals or ceramics). Alternatively, catalyst particles can be made from metal oxides such as Fe3O4, Fe2O4, or FeO, or similar oxides such as cobalt or nickel, or combinations thereof.

Examples of conditioner compounds for use in conjunction with the fluid mixtures of the present invention include thiophene, H2S, other sulfur-containing compounds, or combinations thereof.

Examples of carbonaceous sources for use in conjunction with the fluid mixtures of the present disclosure include, but are not limited to, treated or untreated flare gas, ethanol, methyl formate, propanol, acetic acid, hexane, methanol, or blends of methanol and ethanol. Other liquid carbonaceous sources may also be used, including C2H2, CH3, and CH4.

1B, a detailed description of the injector 14 is shown. In one embodiment, the injector 14 includes a substantially tubular chamber 141 and defines a passageway 142 along which the volatilized fluid mixture is generated and directed to the reactor tube 12. To volatilize or fluidize the mixture, the injector 14 can include a spray tube 16 designed to provide a Venturi effect to generate small droplets from the fluid mixture being introduced from the reservoir 15. In one embodiment, it should be considered that the volatilization or fluidization of the fluid mixture occurs substantially as the fluid exits the distal end 161 of the spray tube 16. In embodiments, the droplets being generated can range from nanoscale sizes to microscale sizes. In one embodiment, to direct the volatilized fluid mixture along the spray tube 16 to the reactor tube 12, a volume of gas, such as H2, He, or any other inert gas, is used to push the volatilized fluid toward the reactor tube 12.

Although the injector 14 is described as being substantially tubular, it should be understood that the injector may be provided in any geometric design so long as it is capable of receiving the atomizing tube 16 and providing a passageway along which the volatilized fluid mixture can be directed into the reactor tube 12.

In addition, it should be noted that the injector 14 of the present disclosure allows for the individual components of the fluid mixture to be introduced into the injector 14 individually, rather than providing them as part of the fluid mixture. In such an embodiment, each component is vaporized individually through an atomizing tube similar to tube 16 and introduced into the injector 14, where they are mixed and subsequently directed along the injector 14 in a manner similar to that described above.

Because the injector 14 is located within the reactor tube 12 and furnace 11, heat being generated within the tube 12 and furnace 11 may have a negative effect on the temperature environment within the injector 14. To insulate the injector 14 from the heat within the reactor tube 12 and furnace 11, a thermal insulation package 17 may be provided around the injector 14. In particular, the thermal insulation package 17 may act to protect the temperature environment along the length of the injector 14.

With the presence of the thermal insulation package 17, the temperature environment within the injector 14 can be reduced to a range capable of influencing the various reactions required for nanostructure growth. To this end, the injector 14 can also include a heating zone A located downstream from the spray tube 16 to provide a sufficient temperature range to allow the formation of catalyst particles from the catalyst precursor. In one embodiment, the heating zone A includes a first heater 18 located downstream of the distal end 161 of the spray tube 16. The heater 18 can be provided, for example, to maintain a temperature range at Tp1 required to decompose the catalyst precursor into its constituent atoms, which then become clusters of catalyst particles on which the nanostructures are subsequently grown. In one embodiment, the heater 18 can be located slightly downstream from Tp1 to maintain the temperature range at Tp1 at a level required to decompose the catalyst precursor. In an embodiment in which ferrocene is used as the precursor, the constituent atoms (i.e., iron particles) are substantially nanoscale in size, but can be generated when the temperature at Tp1 can be maintained in the range of about 200°C to about 300°C.

Heating zone A may further include a second heater 19 disposed downstream of first heater 18 within furnace 11. Heater 19 may be provided to maintain, for example, at Tp2, a temperature range required to decompose the conditioning compound into its constituent atoms. These atoms may be present in clusters of catalyst particles and interact with the clusters to control the size distribution of the catalyst particles, and thus the diameter of the resulting nanostructures. In embodiments where thiophene is used as the conditioning compound, sulfur may be released upon decomposition of thiophene by interacting with the clusters of catalyst particles. In embodiments, heater 19 may be designed to maintain a temperature range at Tp2 of about 700° C. to about 950° C., and to maintain such range at a location slightly downstream of heater 19.

According to one aspect of the invention, Tp2 can be placed at a desired distance from Tp1. Various parameters play a role, and the distance from Tp1 to Tp2 should be such that the flow of the fluid mixture from Tp1 to Tp2, where decomposition of the catalyst precursor occurs, optimizes the amount of decomposition of the conditioning compound to optimize the size distribution of the catalyst particles.

In addition to the specific temperature zones created by the first heater 18 and the second heater 19 within the injector 14, it should be appreciated that the temperature at the distal end 161 of the spray tube 16 must also be maintained within a specific range within the injector 14 to avoid either condensation of the vaporized fluid mixture or uneven flow of the fluid mixture as it exits through the distal end 161 of the spray tube 16. In some embodiments, the temperature at the distal end 161 may need to be maintained between about 100° C. and about 250° C. For example, if the temperature is lower than the indicated range, condensation of the fluid mixture may occur along the walls of the injector 16. As a result, the fluid mixture directed from the injector 16 to the reactor tube 12 may be substantially different than the mixture introduced from the reservoir 15. For example, if the temperature is higher than the indicated range, boiling of the fluid mixture at the distal end 161 may occur, resulting in sputtering and uneven flow of the fluid into the injector 14.

Because the injector 14 may need to maintain a temperature gradient along its length, whether to minimize condensation at the distal end 161 of the spray tube 16, maintain the temperature necessary to allow decomposition of the catalyst precursor at Tp1, or to allow decomposition of the conditioning compound at Tp2, the insulation package 17, in addition to insulating from the reactor tube 12 and furnace 11, can operate to maintain a desired temperature gradient along the injector 14 at each critical location. In one embodiment, the insulation package 17 can be made from quartz or a similar material, or from a porous ceramic material such as zirconia ceramic fiber (e.g., zirconia stabilized boron nitride). Of course, other insulation materials can be used.

In one embodiment, the system 10 is designed so that the fluid mixture exiting the distal end 161 can be introduced into an injector of a second system.

The system 10 is further designed so that either the gas flow or other means breaks down the carbon nanotubes after formation to prevent significant agglomeration, thereby resulting in short carbon nanotube fibers.

Although the making and use of various embodiments of the present invention have been described in detail above, it should be understood that the present invention provides many applicable inventive concepts that can be embodied in a wide range of specific embodiments. The specific embodiments discussed herein are merely illustrative of specific ways to make and use the invention and do not limit the scope of the invention.

Claims (11)

1. A method for producing carbon nanotubes comprising:
(i) obtaining a flare gas comprising a carbonaceous gas;
(ii) treating the flare gas by subjecting the flare gas to one or more processes for removing at least a portion of the excess hydrogen sulfide from the flare gas;
(iii) introducing a mixture of the flare gas, catalyst and hydrogen into a reactor, wherein the reactor is at a temperature sufficient to decompose the carbonaceous gas in the presence of the catalyst into constituent atoms of the carbonaceous gas, wherein the constituent atoms comprise carbon and hydrogen atoms;
(iv) interacting carbon atoms of the carbonaceous gas with a catalyst to produce carbon nanotubes; and (v) recovering the carbon nanotubes. The method of claim 1, wherein the flare gas is obtained from an oil or gas production site, a refinery, a chemical plant, a coal plant, or a landfill. The method of claim 1, wherein the step of treating the flare gas further comprises subjecting the flare gas to one or more processes for removing at least a portion of the excess carbon dioxide and/or carbon monoxide from the flare gas. The method of claim 1, wherein the step of treating the flare gas comprises at least one of: (i) electrochemically reducing at least a portion of the excess hydrogen sulfide in the flare gas to sulfur and then removing it; and (ii) oxidizing at least a portion of the excess hydrogen disulfide in the flare gas to sulfuric acid and then removing it. The method of claim 1, wherein at least a portion of the excess carbon monoxide and/or carbon dioxide in the flare gas is removed from the flare gas. The method of claim 1, wherein the catalyst is ferrocene. 10. The method of claim 1, wherein a portion of the mixture comprising the carbonaceous gas that did not interact with the catalyst to form carbon nanotubes is passed to a second reactor. 8. The process of claim 7, wherein a catalyst amount is recovered from the mixture and then regenerated and introduced into the second reactor or stored for later use. The method of claim 8, wherein the catalyst is regenerated by at least one of: (i) oxidizing the catalyst in air and/or electrochemically stripping the catalyst, dissolving the catalyst in hydrochloric acid to form a hydrochloride salt, and then reacting the hydrochloride salt with sodium cyclopentadienide; and (ii) heating the catalyst to at least 2000°C to volatilize the catalyst, and then depositing the volatilized catalyst. 2. The process of claim 1, wherein the hydrogen introduced into the reactor in step (iii) is hydrogen formed from decomposition of a carbonaceous gas in step (iii) in a separate reactor. 2. The method of claim 1, wherein the carbon nanotubes formed in the reaction vessel prior to exiting the reaction vessel are subjected to impact with (i) one or more high velocity jets of gas, (ii) one or more rotating impellers, (iii) a gas flow across a textured surface, and/or (iv) an array of blunt objects, such that the carbon nanotubes recovered in step (v) are in the form of short carbon nanotube fibers having lengths in the range of 1 mm to about 50 mm.

Images